Changed Chat 5.1 from a SHALL to a SHOULD and added note

[jkaufman-mitre]

🗣 Description

Based on the google update that came out, changed Chat 5.1 to SHOULD to allow for an organization to allow users to install chat apps since Common Controls states to allow apps to be installed if it is allowlisted.

Fixes #222

💭 Motivation and context

Google Product Update and internal discussion

🧪 Testing

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• [ ] Tests have been added and/or modified to cover the changes in this PR.
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✅ Post-merge Checklist

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[adhilto]

I recommend we hold off on this until v0.2 is released.

[jkaufman-mitre]

Sounds good, @adhilto